Digital versatile discs (DVDs) are information storage devices used for storing prerecorded audio information, movies and computer software. The storage mechanism used in DVDs closely resembles that used in compact discs (CDs). DVD players also use the same laser technology as CD players. Briefly, both DVDs and CDs store information as a pattern of pits formed in a metallic substrate. The pit patterns form digital words and can be read by shining a laser beam on the disc surface and detecting the reflected beam. The information storage capacity of a typical DVD, however, is much higher than a CD. Presently available DVDs have a variety of capacities which depend on the technology used to manufacture the discs. Single-layer technologies can be either single or double-sided with capacities of 4.7 gigabytes and 9.4 gigabytes, respectively. Dual layer technologies will soon be available which use single or double sided capacities that hold approximately 8.5 gigabytes per side. This high information storage capacity makes DVDs suitable for storing not only audio information, but also video information and large amounts of computer data as well.
DVD players have many CD player features, such as the ability to play selections in any order desired and the ability to read information from any point on the disc. However, DVDs can store information in several formats. For example, DVDs which are used to store video information, hereinafter called DVD-VIDEO discs, may use various known information compression algorithms, such as MPEG-2 for video compression/decompression. A DVD may also include high fidelity sound as well. In addition, a DVD may also store uncompressed linear pulse code modulated data streams which have sample rates between 48-96 kHz and are sampled at 16 or 24 bits. Still other DVD versions, hereinafter called DVD-ROM discs, can store digital data for computer use, and the data may also be compressed on these discs.
Although DVD-ROM and DVD-VIDEO discs share compression algorithms, the data format on DVD-VIDEO discs is significantly different than the data format found on DVD-ROM discs. One important difference is that the data content on DVD-ROM is platform-specific, while DVD-VIDEO discs operate with a platform independent navigation engine for playing interactive movies. This navigation engine requires that the files on the DVD-VIDEO disc be referenced in a predetermined directory structure.
The specific navigational commands which are recognized by a DVD player are controlled by a device independent language and a set of DVD player parameters which define the current state of the DVD player. The DVD command set, including the aforementioned commands and their definitions, are published in the DVD specification. A copy of the DVD 1.0 Specification for Read-Only Disc Vol. 3, including a more detailed description of all DVD commands, may be obtained, for example, from Toshiba Corp., 1-1 Shibaura 1-Chome, Minato-ku, Tokyo 105-01 Japan.
DVD systems require the ability to transfer large amounts of data from the disc to the playback system. Occasionally, interrupts occur that halt the transfer of data from the disc to the system. These interrupts typically are brief and can be provided for by using memory caching techniques. Memory caching is well know in the computer arts as well in the DVD standard. Memory caching is the technique of reading and retrieving data prior to the time it needs to be used and storing it in very fast memory that is more readily available over the original storage site. This pre-read material is pulled in advance from the DVD disc. Recently, however, an encryption technique has been added that prevents the copying of content on a DVD system.
There are several types of caching systems available. Unfortunately, none works with data that encrypted using the Content Scrambling System (CSS) that is utilized in the DVD Specification. All these caching systems perform read ahead operations in order to minimize the time required to retrieve data for the medium. Each title on a DVD-ROM disc requires the DVD-ROM drive to perform authentication steps, or obtaining a title key, before a sector(s) may be read from the disc. Since the caching system has no knowledge of these title keys, and since consecutive sectors may cross title boundaries, conventional caching techniques cannot be utilized as they fail upon the attempt to read across sectors over multiple titles.
Media-based caching systems using microcode on a DVD-ROM drive system do not have the same problems of reading over titles since they have access to the title key or are allowed to read over titles regardless of the title key. Unfortunately, these caching systems have expensive, nonexpandable cache memory, which limits their use in DVD applications that require large cache memory.
Accordingly, what is needed is a caching system and method that overcomes the prior art problem of reading over multiple titles that are copy protected in order to cache them, which attempt results in a system failure.